Showmeyaa
Bunuel
What is the lowest positive integer that is divisible by each of the odd integers between 15 and 21, inclusive?
(A) 3×17×19×21
(B) 5×17×19×23
(C) 7×15×17×19
(D) 7×15×19×21
(E) 15×17×19×21
Asked: \(\frac{15×17×19×21}{x}\)
What is the smallest value of x? If we can maximize the quotient, we will have the smallest value of x.
1) \(\frac{15×17×19×21}{3×17×19×21}\) = 5
2) \(\frac{15×17×19×21}{5×17×19×23}\) = Not Divisible.
3) \(\frac{15×17×19×21}{7×15×17×19}\) = 3
4) \(\frac{15×17×19×21}{7×15×19×21}\) = Not Divisible.
5) \(\frac{15×17×19×21}{15×17×19×21}\) = 1
Option 1 has the biggest quotient of 5.
So, A) IMO

Here, we are asked what is the least number when divided by each of 15,17,19,21 will lead to a result which is basically asking us to find the LCM of (15,17,19,21).
So \(\frac{15×17×19×21}{x}\) is incorrect.
The question stem means we have to find a number which when divided by each of odd numbers from 15 to 21 wont give any remainder besides 0.
Calculating the LCM of these 4 numbers will lead you to Option C.
On calculation you will also find that the numerator is completely divisible by the denominator.